61x blew up. Tell me what this looks like. (pics inside)

[skithis]

6m6 ignition box on a ported 61x. Westcoast head but was only making 150psi after porting. First tank of 87 octane and kaboom. My old stocker 61x ran on 87 all day long but apparently porting can change detonation characteristics alone. It looks to me like it detonated itself apart but I want to make sure. I was running a size 60 return line restrictor but removed it before I went out the last time.

Also, only 1 cylinder went and the other side is perfect. I think I'm only going to replace 1 piston. Should I be good with a single WSM replacement?

 

[oxnard111]

Don't know about what caused this, but most folks run 91 octane at a minimum

 

[ATS_Aaron]

You answered Most of your own questions: porting changes the reading you will get on a compression gauge. 87 octane is too low.

WSM pistons suck in my opinion. Get Pro X at least.

Aaron

 

[2XLR8]

If your return restrictions have been drilled out and you decided to run with out a restricter this could also contribute to your problem. I prefer wiseco .

 

[jetski9010]

who did the porting? It looks like it might have caught a ring on the exhaust.

 

[ATS_Aaron]

who did the porting? It looks like it might have caught a ring on the exhaust.

We went through that with ATS_Scott's motor. He was running too much compression for his WSM pistons and it snagged a ring. The first time he thought it was just that - a snagged ring so he champhered the hell out of it and ran it for a while at low compression. As soon as he swapped in the high compression domes he snagged a ring again. Something about the heat or the detonation causes the rings to expand more than normal and get caught in the exhaust port. I have not seen this (first hand) with anything but his WSM pistons. I ran too much compression on my DASA motor but caught it before serious damage occured (got some small pitting on one of my Wiseco's).

Oh yeah, I prefer Wiseco's and have them in all my skis, but Pro-X = OEM Yamaha and is pretty good stuff, and a little cheaper if you are counting your nickels.

Aaron